Integrated circuit fabrication relies heavily on frequent and consistent inspection of the structures formed at various stages during the fabrication process. Some of the inspections can be electronic or chemical in nature, but a great many of the inspections that are performed are optical in nature. In other words, the substrates or semiconductor substrates on which the integrated circuits are formed are inspected by collecting electromagnetic radiation such as light received from the substrate, whether that light be reflected from or transmitted through the substrate, and inspecting the properties of the collected light.
There is a continual demand to fabricate integrated circuits at ever-decreasing geometries. The shrinking size of the structures and layers of which integrated circuits are comprised has introduced many new issues which need to be addressed. Many of these issues have to do with optical inspection of the integrated circuits and the substrates on which they are formed.
For example, optical substrate inspection systems typically used relatively long illumination wavelengths to image the structures of the integrated circuit. Such long wavelengths were convenient to use, and tended to adequately resolve the larger structures and thicker layers that were used in earlier integrated circuit designs. However, such longer wavelengths tend to be insufficient to resolve the smaller features of integrated circuits formed according to newer design geometries, and also tend to be insufficient to detect smaller defects, which are now of increasing importance.
One solution to this issue is to use relatively shorter illumination wavelengths than those currently used in optical inspections systems. Shorter illumination wavelengths tend to increase the resolution of the optical system, and thus enable a more complete inspection of small structures and defects. However, shorter illumination wavelengths might also tend to damage one or more of the substrate and the other materials used in integrated circuit fabrication. Such radiation damage was not a problem with the longer wavelengths previously used for optical inspection systems. The use of relatively shorter wavelengths of radiation in other technologies, such as alignment systems, also tends to negatively effect certain integrated circuit materials and structures.
What is needed, therefore, is a system by which integrated circuit structures of smaller sizes and of sensitive materials can be adequately inspected or otherwise processed without damaging the delicate materials of which the structures are formed.